There isn't much more that I can help with unless you have more and better photographs of the additional numbers and proof marks. What you would be looking for are maybe the letters B, U, G, N with crowns over the tops of each and the serial number. These were used between 1924 and 1934 with some carrying on through the later years.
B = rifle proofed in assembled form.
U = final inspection proof.
G = sporting firearm with rifled barrel.
N = indicates Nitro proofing. (from 1933-1939) Also used on military contract rifles for export.

Non-exported receivers had a serial number on the left side of the receiver above the stock line. Exported receivers had the serial number on the bottom of the receiver so that the maker could assign their number to the side.

The caliber could have been placed on the left side of the barrel or underneath on the barrel. Along with this number underneath was the caliber markings: land and groove size (mm) as well as the twist rate (mm) and possibly even the steel maker's name.

If you want to get a thorough grounding in Mausers, I would suggest buying the Ludwig Olson book and the Jon Speed book on Mauser sporting rifles.

I don't recommend tapping the rifle anywhere on it as it will ruin the potential value. As has been pointed out, the stock is not suitable for scope mounts, anyway. It was done but the cheek weld was non-existent.

If you can take the rifle outside and photograph the numbers and proof marks, I might be able to help more. If not, I think that this is the best that I can do.

Chris, the reference was from ‘Old German Target Arms’ Alte Scheibenwaffen by Thompson et.al. You have the complete listing, this information was gathered from old phone books and city directories. I have a good selection of books on German gunmakers and none list anything on Keiss. You can write the gunmakers museum in Suhl, but they know little about the makers of Suhl. Suhl is a town that for a few hundred years has been in the arms making business, but sadly not much has been written about the small makers, of which there were many.

hi nononsense well i took the rifle down again to try and get picts. the resolution i can post here does not show them so i will describe the best i can. edgar kiess suhl and caliber is stampted. the serrial #. beside that 87. the eagle with an n under it below that the eagle witha J under it below that 840 (wich acourding to 2mp should mean august 1940) below that an upside down heart with some lines in it. beside them are two fancy r's inside of a simple scroll. on the receiver ring right side anothe eagle with no letters under it right side serial # under the bolt handle inside the tight curve another plain eagle. no crowns i can see. hopefully this will help. if you would like me to send some better picts of the markings please email me at mmw@gtlakes.com thanks chris

All: Krupp laufstahl is not coarse steel but means barrel steel. Lauf is the German word for barrel. The latch on the side is a Greener side safety - common on drillings and combination guns but uncommon on bolt action rifles.

The African model that Speed refers to is an original Mauser factory sporting rifle model. The original Mauser African Model is very rare. Your rifle, on the other hand, was built by an individual gunmaker and is perhaps even rarer than the Mauser offering but will not command anywhere near the price that a Mauser African Model would command. Still, it is a very nice piece that should be quite desirable among Mauser buffs.

The rifle appears to be a wonderful example of a pre-war product of a fine custom maker in Germany.